Acid Etching Patterns in Naturally-Fractured Carbonate Reservoirs

by
Gopi Nalla, MSE

University of Texas at Austin, 2002
Supervisors: Gary A. Pope
Kamy Sepehrnoori

The objective of my research thesis was to add aqueous chemistry models to a General Purpose Adaptive Reservoir Simulator (GPAS) developed at the University of Texas. GPAS is an implicit, compositional, equation-of-state, parallel simulator that can run efficiently on a range of platforms from a single PC to massively parallel computers or clusters of PCs.

Additional species added to the simulator were tracer, polymer and surfactant. The methodology adopted was to treat each of these species as an aqueous component with special properties calculated in a chemical module. This chemical module takes into account the flux across each grid interface, the phase saturations, phase densities and the upstream locations for each gridblock and uses the one-point upstream weighting numerical method. This is a clever way of calculating the polymer and tracer properties because it imports the flow parameters already calculated in the host simulator. The convection part of the mass conservation equation is solved explicitly at the end of each Newtonian iteration for every timestep. The polymer properties partially modeled in the chemical module are aqueous phase viscosity, polymer adsorption, aqueous phase permeability reduction and the inaccessible pore volume.

Comparisons with analytical solutions were made to verify the correctness of the mathematical formulation, the finite-difference schemes and the code and to compare the accuracy and efficiency of the different methods. Both continuous injection and tracer slug concentration profiles and history numerical results were compared with analytical solutions and with the UTCHEM simulator numerical output and were generally in good agreement. Numerical results from GPAS for polymer flooding were also compared with analytical solution.

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